Sleep deprivation significantly impairs cognitive functions such as psychomotor speed, attention, working memory, and higher cognitive abilities. Chronic sleep restriction leads to cumulative cognitive deficits without the individual's awareness. Functional neuroimaging shows widespread brain region changes, including the prefrontal cortex, parietal areas, and thalamus. Individual differences in cognitive vulnerability to sleep loss may involve prefrontal and parietal cortices and genes regulating sleep homeostasis and circadian rhythms. Sleep deprivation increases accident risk, with effects comparable to alcohol consumption. Sleep deprivation reduces alertness and impairs psychomotor functions, similar to alcohol intoxication. Sleep deprivation affects all modes of transportation and safety-sensitive activities. The neural basis of these risks is better understood through experimental studies of sleep deprivation's effects on cognitive functions. Sleep deprivation increases sleep propensity, measured by reduced sleep latency. Sleep-deprived individuals experience microsleeps and wake state instability, leading to cognitive variability. The state instability hypothesis suggests that cognitive performance variability during sleep deprivation is due to unstable wake states. Sleep deprivation impairs attention, working memory, and verbal learning. Functional neuroimaging studies show reduced activation in the prefrontal cortex, parietal regions, and thalamus. PET and fMRI studies reveal decreased metabolic rates and neural activity in sleep-deprived individuals. Sleep deprivation affects emotional memory and processing, with impaired recollection of emotional stimuli. Reward expectations are also affected, with increased anticipation of higher rewards and reduced neural responses to losses. Individual differences in cognitive vulnerability to sleep loss are evident, with some individuals showing greater resistance. ASL perfusion fMRI provides a noninvasive method to quantify cerebral blood flow, useful for sleep deprivation studies. Chronic partial sleep restriction, common in modern society, leads to cumulative cognitive deficits. Sleep restriction to less than 7 hours per night results in significant cognitive impairments. The critical period for cognitive deficits is around 15.84 hours of continuous wakefulness. Sleep deprivation studies highlight the importance of sleep for maintaining normal waking cognitive functions. Individual differences in sleep need and vulnerability to sleep loss affect cognitive performance. The findings suggest that sleep is essential for cognitive function and that sleep deprivation has significant consequences for cognitive and behavioral performance.Sleep deprivation significantly impairs cognitive functions such as psychomotor speed, attention, working memory, and higher cognitive abilities. Chronic sleep restriction leads to cumulative cognitive deficits without the individual's awareness. Functional neuroimaging shows widespread brain region changes, including the prefrontal cortex, parietal areas, and thalamus. Individual differences in cognitive vulnerability to sleep loss may involve prefrontal and parietal cortices and genes regulating sleep homeostasis and circadian rhythms. Sleep deprivation increases accident risk, with effects comparable to alcohol consumption. Sleep deprivation reduces alertness and impairs psychomotor functions, similar to alcohol intoxication. Sleep deprivation affects all modes of transportation and safety-sensitive activities. The neural basis of these risks is better understood through experimental studies of sleep deprivation's effects on cognitive functions. Sleep deprivation increases sleep propensity, measured by reduced sleep latency. Sleep-deprived individuals experience microsleeps and wake state instability, leading to cognitive variability. The state instability hypothesis suggests that cognitive performance variability during sleep deprivation is due to unstable wake states. Sleep deprivation impairs attention, working memory, and verbal learning. Functional neuroimaging studies show reduced activation in the prefrontal cortex, parietal regions, and thalamus. PET and fMRI studies reveal decreased metabolic rates and neural activity in sleep-deprived individuals. Sleep deprivation affects emotional memory and processing, with impaired recollection of emotional stimuli. Reward expectations are also affected, with increased anticipation of higher rewards and reduced neural responses to losses. Individual differences in cognitive vulnerability to sleep loss are evident, with some individuals showing greater resistance. ASL perfusion fMRI provides a noninvasive method to quantify cerebral blood flow, useful for sleep deprivation studies. Chronic partial sleep restriction, common in modern society, leads to cumulative cognitive deficits. Sleep restriction to less than 7 hours per night results in significant cognitive impairments. The critical period for cognitive deficits is around 15.84 hours of continuous wakefulness. Sleep deprivation studies highlight the importance of sleep for maintaining normal waking cognitive functions. Individual differences in sleep need and vulnerability to sleep loss affect cognitive performance. The findings suggest that sleep is essential for cognitive function and that sleep deprivation has significant consequences for cognitive and behavioral performance.